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Old 23rd October 2003, 07:11 AM   #1
Jesse is offline Jesse  Taiwan
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Default I burned my Aleph 3! Please help!

Hello Pass fans,

I somehow burned my Aleph 3 clone few days ago.

Now the right channel outputs +24VDC.
I changed the 3 IRF9610 and 2 MPSA18.
I checked the IRFP244s. Seems to be good.
But still no help.

The voltage across R106 and R108 is now only 1V.
The voltage at the D-leg of Q103 is 3V.
The voltage at the G-leg of Q102 is 9V.
The voltage across Q105 is 3.5V
The voltage across Z103 is 4V

Could anyone help please?

Thanks!

Jesse
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Old 23rd October 2003, 07:53 AM   #2
Netlist is offline Netlist  Belgium
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Did you replace Z103?

Strange that you have 9V at the Gate of Q102
Is that measured with respect to ground?

/Hugo
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Old 23rd October 2003, 09:01 AM   #3
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Default z103 was broken

i think so.
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Old 23rd October 2003, 09:21 AM   #4
Jesse is offline Jesse  Taiwan
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Hello Hugo,

Yes, the 9V is measured respect to ground.

Thsnks Hugo and John!

I'll replace the Z103 tonight and let you know the results.

Cheers,
Jesse
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Old 23rd October 2003, 12:17 PM   #5
Jesse is offline Jesse  Taiwan
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I changed Z103 but no help.

What else could be wrong?

Should I change the MOSFETs?


Jesse
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Old 23rd October 2003, 12:32 PM   #6
Netlist is offline Netlist  Belgium
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What happened that caused the amp to misbehave?
Assuming you have + and - 25V supply,
I still guess your problem is in the front-end.
There is not a lot that can break in the input.
Make sure you connected everything correctly. (Bad solderings, earth)
What's the voltage across the feedback resistor?

/Hugo
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Old 23rd October 2003, 03:18 PM   #7
Jesse is offline Jesse  Taiwan
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Hi Guys,

I changed the MOSFETs (all 4 of them) anyway.
Now the output becomes -24V???

Q106 is VERY hot in a few seconds after powered on?

What else can go wrong?

Jesse
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Old 23rd October 2003, 03:26 PM   #8
Jesse is offline Jesse  Taiwan
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Hi Hugo,

I did something with my preamp and after that the Aleph burned. So I also think the problem is from the front end.

Yes, the supply rails are +/-25V.

By the way, isn't there two zeners to protect the circuit???
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Old 23rd October 2003, 03:37 PM   #9
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I had a similar problem when I built my power amps, all the components we fine but the thing didnt work. The problem was in the PCB there was a tiny tiny break in one of the tracks (you couldnt see it but measure it you could), this sorted out the thing sang like all the other 4 channels did. Anyway could it be possible that you have got all the components working but in the listening process you managed to burn out a track that wasnt etched verywell. My boards were my 1st so they had some discontinueties your mite be fine. Anyway just my $0.02.
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Old 23rd October 2003, 04:33 PM   #10
Netlist is offline Netlist  Belgium
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Yes, the zeners are there to protect the diff-pair from overvoltage and spikes, but they also can break.

You'll have to check your connections IMO.
Be careful with mosfets and ESD. Discharge the PSU-caps before
soldering something in and out. There's a good chance that 5 to 10 V remains at them after you power off. Get rid of that voltage
or you might damage your new fets when soldering them in.
You could try to disconnect your output mosfets and only power up your front-end.
Work carefully, try to power up with a variac and yes, check the pcb for bad traces. (Can be very difficult)
Any pictures perhaps?

/Hugo
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